Method of stripping copper plate



Patented Sept. 24, 1940 g 2,215,5oi mz'rnonor s'rmrrnvc cornea PLATEWilliam W. Hnnlock, Toledo, Ohio, assignor to The Gerity-Adrian Mfg.00., Adrian, Mich, a corporation of Michigan No Drawing. ApplicationJune 3i),1938,

Serial No. 216,770

6 Claims. .(01 -97) This invention relates to a method of strippingcopper plate or similar coatings from a basis metal article.

It has heretofore been the custom in stripping copper plate from, forexample, zincdie castings, to rely primarily on mechanical removal suchas bufling, grinding or the like. It has also been proposed to immersethe copper plated article in a relatively strong acid solution to dislsolve the copper, with orwithout the use of electric current. Each ofthese methods possesses the disadvantage that it will not accomplishsatisfactory results when used on an article having a highly irregularconfiguration. For example. in stripping copper plate from a die castradiator grille for an automobile, certain parts of the grille areinaccessible to a grinding or bufling wheel and mechanical removal istherefore unsatisfactory. In articles such as these, the thickness ofthe plated metal is non-uniform due to the irregular configuration. Ifit is attempted to strip the copper by strong acid, it will be foundthat the thin portions of the copper plate are removed first and thethicker parts removed' only 3 after the acid has attacked the basismetal andaltered the surface configuration of the article.

The present invention has as its primary object to overcome thedisadvantages of each of the above methods and, by proper control, tore- 3 move copper plate from irregular articles successfully and withoutattacking the basis metal.

The invention consists in immersing the copper plated article in asolution which contains a material which will react with the copper to315 forma compound thereof, and subsequently immersing the article in asolution capable of dis-. solving the compound so formed. Specificdetails of the method and its advantages will become apparent from thefollowing specification.

40 A copper plated article such, for example, as a die casting, isimmersed in a solution containing a sulfide capable of reacting with thecopper to form copper sulfide. The dissolved sulfide may be any of thesulfides or polysulfides of hydrogen,

ammonium, sodium or potassium or any others which will react to form asulfide of copper. The article is left in this solution until thesurface is completely black and until all of the copper has been actedupon. The length of time necessary 60 for the reaction depends on theconcentration of the solution, thickness of the copper 'plate,temperature and other factors, but can be readily determined by trialand error.

The article, which now has a surface coatin 56 of black copper sulfide,is ne t in a What I claim as new and desire to secure by alkali metal;

second solution containing a material capable of reacting with thecopper sulfide to remove it from the article. Sodium or potassium'cyanides have been found suitable for this purpose.

If, on inspection of the article as it is removed 5 from the cyanidesolution, it is found that some copper still remains on the article, theprocess may be repeated. By maintaining the pH value 1 of the initialsolution such that the solution is neutral or slightly alkaline, thedissolved sulfides 10 either do not react with the zinc of the basismetal or react so slowly that no damage is done to the surface of thearticle. It is possible for the sulfides to combine with the copper inacid solutions, but the higher the acid content, the 15 more readily thebase metal is attacked.

The removal of the copper sulfide from the article is accelerated bymaintaining a relatively highcyanide concentration in the secondsolution. 2

United States letters Patent is:

1. The method of stripping copper plate which comprises immersing aplated zinc article in a substantially neutral solution containing oneof the groupconsisting of the sulfides and polysulfides of hydrogen,ammonium, sodium and potasslum and subsequently immersing the article ina solution containing cyanide of an alkali metal so which reacts withthe copper sulfide to remove it from the article.

2. The method in accordance with claim 1 in which the first solutioncontains sulfide of an a. The method in accordance with claim 1, in 35which the first solution contains hydrogen sulfide. 4. The method inaccordance with claim 1, in which the second solution contains sodiumcyanide.

f 5. The method in accordance with claim 1, in which the second solutioncontains potassium cyanide.

6. The method of stripping copper plate from a zinc die casting whichcomprises immersing the plated casting in a solution which is not acidnor more than slightly alkaline, and comprises sulfide of an alkalimetal, continuing the action until the metallic copper is converted intocopper sulfide, thereafter immersing the article in a solutioncontaining cyanide of an alkali metal, and continuing this immersionuntil the copper sulfide is dissolved in said solution.

WJILIAMW.HUNLOCK.

